Hero 5 leaking issue!

Hi! I've taken my Hero 5 out into the water a couple of times without a problem, but recently I took it out to the water park during my holiday, and water seems to have seeped in, despite all the caps being shut tight! It won't even turn on now - aren't these guys supposed to be waterproof? Really upset right now as it was a farewell gift from my siblings when I migrated abroad. Any help is greatly appreciated!